File photo taken on June 24, 2014 shows US whistleblower Edward Snowden speaking to European officials via videoconference during a parliamentary hearing at the Council of Europe in Strasbourg, eastern France

US fugitive Edward Snowden, who was granted asylum by Moscow after revealing the extent of US global surveillance, has been reunited with his girlfriend in Russia, his lawyer said Saturday.

Snowden's longtime partner, American dancer Lindsay Mills, joined him in Moscow in July, it emerged Friday.

"Love is love," Snowden's lawyer Anatoly Kucherena told AFP. "She lives with him when she comes here. Moral support is very important for Edward."

He said Mills does not live in Russia permanently because of visa constraints but visits frequently.

The couple, who previously lived in Hawaii, have been busy exploring Russia, he added. "They go to theatres and cultural events together."

Kucherena spoke after a documentary by Laura Poitras, shown at advance screenings in New York late Friday, revealed Mills had joined him in Moscow over the summer.

The two-hour documentary -- due for release on October 24 -- paints an intimate and sympathetic portrait of Snowden holed up in a Hong Kong hotel in June 2013 as he blows the whistle on National Security Agency dealings and then plots his escape.

Mills is shown preparing dinner with Snowden in a wood-panelled kitchen, but the couple's conversation is not recorded and she is not interviewed.

The whereabouts of Mills, who once referred to herself on a blog as "a world-traveling, pole-dancing super hero", were not previously known.

She has never spoken publicly about her boyfriend, who has been charged in the United States with espionage, and some reports had suggested that the couple had split.

'I may not be coming back'

But the documentary "Citizenfour" hints at a much closer union.

Image from Lindsay Mills' Flickr stream.

It shows Snowden breaking the news online to Mills from Hong Kong that he would not be back anytime soon after she told him agents had turned up at their home in Hawaii, suspicious about his absence from work.

"It's a tough situation," he says, close to tears on his hotel bed after telling Mills that he "may not be coming back".

"She has no idea what I'm doing," he says. He says he feels "badly" about simply disappearing while she was on vacation but said he did it to protect her.

After the NSA surveillance story breaks, the couple are shown to be still in touch.

Mills tells him that his rent cheques are no longer going through, which he calls "strange" because they had been set up automatically, and that trucks are all over the street outside their home.

"Citizenfour" shows Snowden at the Mira hotel in Hong Kong during interviews with journalists from the Guardian newspaper in 2013 that resulted in a series of stories about the extent of phone and Internet surveillance by the British and US governments.

There are some astonishing nuggets of information, such as his assertion that at NSA he could watch drone strikes and surveillance at anytime on his desktop -- -- "lots of them in all these countries".

Snowden is reluctant to talk about himself, but Poitras shows a man committed to exposing mass data surveillance, who says he would rather risk prison than have his intellectual freedom curtailed.

Paranoia and disguises

He patiently explains the extent of the surveillance and how it worked. Yet he admits he is nervous, and appears worried and jumpy.

The extent of Snowden's paranoia about being monitored is also laid bare.

He logs onto his laptop under a hood, in case any hidden camera can see his passwords.

He unplugs the hotel room phone, then makes a wry remark when the hotel starts testing the fire alarm.

"Maybe they got wind they couldn't listen in to us by the phone any more," he said.

They discuss when Snowden should go public as the person responsible for the intelligence leak, and he admits that he's eating less, and worried about someone "busting through the door".

Snowden watches the magnitude of his intelligence leaks unfold on TV. There are moments of levity, but the tension builds as he plots his escape from an advancing horde of journalists.

With TV in the background comparing the NSA story to a John Le Carre spy novel, Snowden tests out disguises in the mirror, by shaving and gelling back his hair. He also experiments with using an umbrella to shield part of his face.

The documentary, with its tantalising glimpses of Snowden's behind-the-scenes life, ends with journalist-activist Glenn Greenwald going back to Moscow to meet him.